<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.12"></script>
</head>
<body>

<div id="app">
    <button v-on:click="sayhi">click here</button>
</div>


<script>
    var vm = new Vue({//
        el:"#app",
        data: {
            message: "hello"
        },
        methods: {
            sayhi: function(event){
                alert(this.message);
            }
        },
       
    })
</script>


</body>
</html>